Physics

Picosecond-resolved entanglement distribution over an urban free-space channel

Alessandro Laneve, Fabrizio Cienzo, Santiago Gomez, et al.

Featured August 3, 2026

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Simply

A new super-accurate clock system helps send tricky, fast-changing quantum signals between buildings in a city, making future quantum internet connections more reliable by keeping their special connections intact.

In depth

The paper demonstrates the faithful distribution of a fast-evolving entangled state over a 270 m urban free-space channel. This is achieved by integrating a novel synchronization device that provides sub-50 ps timing accuracy, which is crucial for resolving the picosecond-scale entanglement dynamics of the quantum dot source and maintaining high entanglement fidelity.

Key Takeaways

1
The study introduces a novel one-way time-frequency transfer synchronization system, achieving sub-50 ps timing accuracy (39 ps FWHM jitter) over a 270 m urban free-space link.
2
The developed system enables the time-resolved distribution and characterization of fast-evolving entangled states generated by a quantum dot, overcoming limitations of traditional GPS synchronization (400 ps jitter).
3
The paper demonstrates that high fully entangled fraction (FEF) (up to 88.7%) and Bell state fidelity can be maintained for time-evolving states distributed through noisy urban channels, paving the way for practical quantum communication applications.

Conceptual Flow

HIGH LEVEL

High-Precision Synchronization for Quantum Links

To send super-fast quantum signals without losing their special connection, the paper built a special clock that keeps two distant labs perfectly in sync, much better than GPS.

Master Clock Signal

Send Over Air

Receive & Sync

Precise Timing

Faithful Distribution of Evolving Entanglement

Because of the super-accurate clock, the paper could successfully send a 'wobbly' quantum signal between buildings, keeping its special quantum connection intact, which old clocks couldn't do.

Wobbly Quantum Signal

Sent with New Sync

Received Wobbly Signal

Special Connection Maintained